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Production systems literature usually attributes throughput losses to two reasons: unreliable equipment and random part processing time (also referred to as machine cycle time). In practice, howeve...

Estimates of production systems performance metrics, such as machine efficiency, e, system throughput, TP, lead time, LT, and work-in-process, WIP, are necessary for evaluating effectiveness of pot...

Building on the Theory of Constraints (TOC) in the service context and drawing on internal and external service profit chain literature, we explore the role of throughput orientation at the manager...

Unbalanced, unreliable (UR), unpaced, merging assembly lines are simulated in this study with varying line lengths, buffer storage capacities, imbalance degrees and unequal mean operation time configurations and uneven buffer capacity (BC) allocation. This paper contributes to the literature by suggesting that, in many cases, imbalance can improve merging lines’ performance, as compared to a corresponding balanced merging line. It was found that an inverted bowl or descending patterns for mean operation times (MTs), and an inverted bowl (concentrating BC towards the centre of the line) or an ascending pattern for buffer allocation, result in higher throughput (TR). In terms of average buffer level (ABL), the best pattern is a monotone decreasing order regarding MTs and a monotone increasing order with respect to BC allocation. Additionally, it was found that when considering a profit function, the best performing patterns for UR lines tend to be the patterns that reduce ABL, even when considering very low inventory holding costs; contrary to the behaviour of the profit function in reliable lines, which suggests that either patterns that increase TR or reduce ABL can lead to a good performance, depending on the values of the unitary inventory holding costs.

International audience; Storage and retrieval automation has progressed rapidly. One such popular storage and retrieval system deploys two passing aisle-bound cranes. Each crane can access every location in the rack. To pass the other crane and prevent collision, each crane has to timely move the platform to an appropriate level and simultaneously rotate it. We develop a queuing model with preemptive-resume interrupted service to estimate the system response time (and hence throughput capacity) while considering two I/O point positions, random storage, and a crane assignment policy where all requests are shared between the cranes. The analytical models are validated with simulation based on the data from real cases. We find that a design with I/O points located in the middle of the rack will increase the interference, but it has a high relative throughput because of the reduced expected travel time. Compared with a system with one crane, a two-crane system has interference, but it can improve the system efficiency, especially in large systems with high job arrival rates. The model can be extended to other systems where multiple cranes are used in a single travel aisle with crane interference, e.g. passing cranes operating in a container stack lane.

Many production systems are multistate, with a finite number of performance levels that are between perfect functioning and complete failure. Importance measures are often used in the maintenance planning of complicated systems, to observe the criticalities of components, reveal the system weakness, and thus to guide the allocation of limited maintenance resources. This paper compares several commonly used importance measures for multistate systems, and investigates their effectiveness and limitations with a simple example. These existing measures focus on the states of a system at some moment, while ignoring the dynamic behaviours in the long-term. For a production system, however, its throughput in a certain period, rather than the instantaneous performance, is the system property of interest. Therefore, two new long-term throughput-based importance measures: total throughput importance measure and maintenance effect importance measure are proposed in this paper, to answer the questions about the criticalities of different components and the long-term effects of successful maintenance activities on the throughput of a production system in a certain period. A case study on an offshore production system is conducted, to illustrate how the new importance measures work and what kind of implications can be provided to the maintenance crew. This is an [Original Manuscript] of an article published by Taylor & Francis in [International Journal of Production Research] on [28 Feb 2018], available at https://doi.org/10.1080/00207543.2018.1442947

The operational efficiency of handling resources plays an important role in promoting container flows at a container terminal. As these handling resources operate on specific yard layouts, a well-d...

When designing a new large manufacturing system with high throughput, the corporation should weigh several factors: the capital investment cost, the system’s responsiveness to future varying market demand, the production losses due to disruptive events, and the product quality. These performance metrics depend heavily on the system configuration. In this paper, typical configurations of large-volume manufacturing systems for mechanical products are compared from cost, responsiveness and product quality perspectives. In addition to traditional serial lines and pure parallel systems, we also discuss two practical configurations – parallel serial lines, and reconfigurable manufacturing systems. The results offer managerial insights for selecting the system configuration that creates the maximum economic value over the lifetime of the system, and fits the corporation needs and culture.

We present an analytic model to assess the performance of a trip-based material handling system with multiple devices dispatched according to the modified-first-come-first-served rule. A key element of the model is the analytic treatment of empty trips based on whether they are device- or station-initiated. The model is evaluated against simulation results using multiple layout configurations and devices at different levels of utilisation. In developing the analytic model, we also investigate the role and impact of device-initiated dispatching vs. station-initiated dispatching, and show results that shed light on conflicting views presented in the literature on this subject. The proposed analytic model can be used to rapidly evaluate alternative handling systems and to conduct various ‘what if’ analyses; it performs reasonably well across a range of systems that were tested via simulation. In evaluating the accuracy of the model, we introduce a unique and more effective technique based on the allocation of empty trips out of each station. In addition, we propose an approximate but simple method to check for system stability.

The clearing function models the non-linear relationship between work-in-process and throughput and has been proposed for production planning in environments with queuing (congestion) effects. One ...

This paper pursues two goals: (a) Define a class of widely used in practice flexible manufacturing systems, referred to as Multi-Job Production (MJP) and formulate industrially motivated problems related to their performance. (b) Provide initial results concerning some of these problems pertaining to analysis of the throughput and bottlenecks of MJP serial lines as functions of the product-mix. In MJP systems, all job-types are processed by the same sequence of manufacturing operations, but with different processing time at some or all machines. To analyze MJP with unreliable machines, we introduce the work-based model of production systems, which is insensitive to whether single- or multi-job manufacturing takes place. Based on this model, we investigate the performance of MJP lines as a function of the product-mix. We show, in particular, that for the so-called conflicting jobs there exists a range of product-mixes, wherein the throughput of MJP is larger than that of any constituent job-type manufactured in a single-job regime. To characterize the global behavior of MJP lines, we introduce the Product-Mix Performance Portrait, which represents the system properties for all product-mixes and which can be used for operations management. Finally, we report the results of an application at an automotive assembly plant.

Constant Work-in-Process (ConWIP) is a card-based control system that was developed for simple flow shops – a lack of load-balancing capabilities hinders its application to more complex shops. In contrast, load balancing is an integral part of Workload Control, a production planning and control concept developed for high-variety environments. One means of load balancing evident in the Workload Control literature is through the use of a capacity slack-based backlog-sequencing rule. This study therefore investigates the potential of the backlog-sequencing decision to improve load balancing in the context of ConWIP, thereby making it suitable for more complex, high-variety environments. Using simulation, we demonstrate that: (i) the choice of backlog-sequencing rule significantly impacts throughput times and tardiness-related performance measures; and (ii) capacity slack-based sequencing rules achieve significant performance improvements over ‘classical’ ConWIP backlog-sequencing rules. These results significantly extend the applicability of ConWIP. Results from the Workload Control literature however do not directly translate across to ConWIP. The simplified release procedure of ConWIP makes backlog-sequencing based on planned release dates dysfunctional. This negatively impacts the performance of modified capacity slack-based sequencing rules that were recently shown to be the best choice for Workload Control. info:eu-repo/semantics/publishedVersion

Container terminal performance is largely determined by its design decisions, which include the number and type of quay cranes (QCs), stack cranes (SCs), transport vehicles, vehicle travel path, and stack layout. The terminal design process is complex because it is affected by factors such as topological constraints, stochastic interactions among the quayside, vehicle transport and stackside operations. Further, the orientation of the stack layout (parallel or perpendicular to the quayside) plays an important role in the throughput time performance of the terminals. Previous studies in this area typically use deterministic optimization or probabilistic travel time models to analyze the effect of stack layout on terminal throughput times, and ignore the stochastic interactions among the resources. It is unclear if stochastic interactions have an impact on the optimal stack layout. In this research, we capture the stochasticity with an integrated queuing network modeling approach to analyze the performance of container terminals with parallel stack layout using automated lifting vehicles (ALVs). Using this model, we investigate 1008 parallel stack layout configurations in terms of throughput times and determine the optimal stack layout configuration. We also find that, assuming an identical width of the internal transport area, container terminals with parallel stack layout perform better (from 4% - 12% in terms of container throughput times) than terminals with a perpendicular stack layout.

This paper focuses on performance changes stemming from a series of lean interventions in a medical laboratory. This research is one of the first to link a series of lean interventions and performance over time. In a mixed-method case study, six years of patient-related throughput data, retrieved from a laboratory computer database, are analysed. Three distinct periods with significant differences in throughput time performance can be distinguished. Semi-structured interviews were held to investigate the lean interventions preceding the performance changes. Given the long-term nature of the study, the event history calendar method was applied to enhance the respondents' recall and reliability. A single lean intervention, among the hundreds that took place, was supposed to cause the main reduction in throughput times. It concentrated on improving process flow through the removal of batching, a source of artificial variability. A later major intervention, the introduction of flow-focused machinery, had mixed effects and initial performance gains were not sustained. The results show that ongoing series of interventions do not always lead to ongoing performance improvements in terms of throughput times but support theories emphasising the importance of variability reduction.

Major ports contain multiple container terminals, sea terminals, train, truck and barge terminal, and empty container depots, operated by different companies. Port authorities try to streamline inter terminal container transport (ITT) within congested port areas by offering expensive common road and rail infrastructure. Alternatively, individual stakeholders can set up private or collaborative container transport systems. This paper develops a framework to analyse and determine feasibility conditions of a common ITT system in a port area, depending on total transport volumes. First, we develop a simulation model to evaluate the costs of transporting containers using different modes of transport including trucks, automated guided vehicles, and multi trailer systems. Next, the required number of vehicles per mode is determined for a given throughput and waiting time. The results of the simulation are used in a game-theoretic setting to determine the cost savings per stakeholder operating in a coalition. By comparing cost savings for all possible coalitions, it is possible to determine, for each stakeholder, the attractiveness of using a common system. We find the coalitions that result in the highest savings and compare them with the infrastructure cost required to realise them. We apply the method to determine the feasibility of a common ITT system for terminals in the Port of Rotterdam and show that it only pays off in case of high demand for container transports.

Recently, the estimation and monitoring of manufacturing key performance indicators (KPIs) have drawn significant attention. In this article, a KPI estimation and monitoring method using a multi-output Gaussian process (MGP) is proposed. The Gaussian process (GP) is an effective non-parametric flexible tool for data-driven statistical modelling for various systems. The unique features of the proposed method is that the MGP enjoys the high flexibility and desirable analytical properties of the GP while also capturing the correlation between different KPIs, thus providing better estimation accuracy and error quantification. The advantageous features of the proposed method are demonstrated through a numerical study as well as a case study with real world data in the estimation and monitoring of throughput for a multiclass production operation.

We propose a new approach to forecasting total port container throughput: to generate forecasts based on each of the port’s terminals and aggregate them into the total throughput forecast. We forecast the demand for total container throughput at the Indonesia’s largest seaport Tanjung Priok Port, employing SARIMA, the additive and multiplicative Seasonal Holt-Winters (MSHW) and the Vector Error Correction Model (VECM) on the monthly port and individual terminal container throughput time series between 2003 and 2013. The performance of forecasting models is evaluated based on mean absolute error and root mean squared error. Our results show that the MSHW model produces the most accurate forecasts of total container throughput, whereas SARIMA generates the worst in-sample model fit. The VECM provides the best model fits and forecasts for individual terminals. Our results report that the total container throughput forecasts based on modelling the total throughput time series are consistently better than thos...

The aim of this research is to demonstrate how human learning models can be integrated into discrete event simulation to examine ramp-up time differences between serial and parallel flow production strategies. The experimental model examined three levels of learning rate and minimum cycle times. Results show that while the parallel flow system had longer ramp-up times than serial flow systems, they also had higher maximum throughput capacity. As a result, the parallel flow system frequently outperformed lines within the first weeks of operation. There is a critical lack of empirical evidence or methods that would allow designers to accurately determine what the critical learning parameters might be in their specific operations, and further research is needed to create predictive tools in this important area.

Rapid and cost-effective scalability of the throughput of manufacturing systems is an invaluable feature for the management of manufacturing enterprises. System design for scalability allows the enterprise to build a manufacturing system to supply the current demand, and upgrade its throughput in the future, in a cost-effective manner, to meet possible higher market demand in a timely manner. To possess this capability, the manufacturing system must be designed at the outset for future expansions in its throughput to enable growths in supply exactly when needed by the market. A mathematical method that maximises the system throughput after reconfiguration is proposed, and an industrial case is presented to validate the method. The paper offers a set of principles for system design for scalability to guide designers of modern manufacturing systems.

In this paper, we propose a factory-level dynamic operator allocation policy called the bubble allocation policy. This policy is commonly implemented in labour-intensive industries in the presence of different operator speeds, high labour turnover, and learning effects. We prove the optimality of bubble allocation in several typical scenarios under deterministic and exponential processing time and different operator speed assumptions. When labour turnover and learning effects were considered, the effects of the bubble allocation were verified through simulation. Bubble allocation had a more significant positive effect on system throughput than the passive operator allocation policy. The positive effects of bubble allocation are enhanced with a larger production system scale (more parallel lines and more stations), higher turnover rate and slower learning process. Compared with active allocation policies such as work-sharing policy, bubble allocation policy has no requirements for additional cross-training...

At any distribution centre (DC), the decision of whether to synchronise inbound and outbound flows for cross-docking, or to decouple these flows by maintaining inventory, has a significant impact on supply chain performance. Key drivers of this decision, in turn, are the sizes of the discrete lots that comprise the flows. Thus, we formulate an original optimisation model that determines order lot-sizing decisions to minimise, for given constant arc flows, the sum of ordering cost and pipeline inventory cost on arcs and buffer inventory at DCs. The model employs an average throughput as a surrogate to estimate buffer inventory at facilities at which synchronisation is not economical and therefore serves to decouple inbound and outbound flows. Perfect lot-for-lot matching of shipments would impose very restrictive constraints on supply chain operations, but equality of average throughput indicates an innovative, relaxed mode of synchronisation. This mode is practicable for cross-docking by means of bulk-bre...

Wafer fabrication is characterised with advanced equipment, complex processes and high cost. Good production output, measured by yield given total throughput, should rapidly increase while considering the associated cost. Yield improvement models based on inspection usually consider the effect of excursion monitoring, while this work considers the effect of learning from experience as well. It assumes a production model where each machine’s output is inspected via wafers it processes, triggering repair if required. The yield improvement is modelled as a function of machine’s quality performance, accumulated inspections, inspection capacity and inspection rate. It exhibits a sigmoid shape curve with slow rise in startup, acceleration in ramp and almost a plateau in high volume manufacturing. Higher inspection rate enables more inspections over time, faster learning and higher yield. Yet, higher inspection rate at constant capacity prolongs the response time and can further drive lower yield. Clearly, highe...

An analytical model for evaluating the throughput of two-machine lines, characterised by intermediate buffer with finite capacity, deterministic processing times and multiple failure modes for each machine is presented in this paper. Both operation-dependent failure and time-dependent failure are captured in a unique model as extension of the existing literature that was dealing with either one of them. Each machine has two failure modes, one is operation-dependent and the other is time-dependent. Time to failure and time to repair are assumed to be geometrically distributed. The presented method calculates the steady-state probabilities of the manufacturing system with a computational effort that depends only on the number of failure modes and not on the buffer capacity. A performance comparison of the proposed model with existing techniques is also reported, the aim is to show the error introduced by an analytical model that considers the operation-dependent failure mode as approximation of the time-dep...

Global competition and increasing customer expectations are forcing automobile manufacturers to improve their operations. Maintenance, being one of the most critical components in many industries, has a direct impact on the improvement of the overall production performance. In this paper, we introduce an anticipative plant-level maintenance decision support system (APMDSS) that provides guidance on corrective and preventive maintenance priorities based on the equipment bottleneck ranks with the objective of improving daily plant throughput. APMDSS anticipates the plant dynamics (i.e. bottlenecks, hourly buffer levels and likelihood of machine breakdowns) for upcoming shifts using starting state information of the production shift (e.g. equipment maintenance history, operational status of machines, buffer levels and scheduled production model mix). We also evaluate the performance of APMDSS using real data from an automotive body shop experiencing routine throughput difficulties due to frequent machine bre...

Technological developments in the global supply chain have changed processes in warehousing. This reflects in short response time in handling the orders, which has a consequence on high automation degree in warehousing. An important part of automated warehouses is presented by shuttle-based storage and retrieval systems (SBS/RS), which are used in practice when demand for the throughput capacity is high. In this paper, analytical travel time model for the computation of cycle times for double-deep SBS/RS is presented. The advantage of the double-deep SBS/RS is that fewer aisles are needed, which results in a more efficient use of floor space. The proposed model considers the real operating characteristics of the elevators lifting table and the shuttle carrier with the condition of rearranging blocking totes to the nearest free storage location during the retrieval process of the shuttle carrier. Assuming uniform distributed storage locations and the probability theory, the expressions for the single and d...

Efficient handling of containers at a terminal can reduce the overall vessel sojourn times and minimise operational costs. The internal transport of containers in these terminals is performed by vehicles that share a common guide path. The throughput capacity of a terminal may increase by increasing the number of vehicles; however, simultaneously congestion may reduce the effective vehicle speed. We model this situation accurately using a traffic flow-based closed queuing network model. The vehicle internal transport is modelled using a load-dependent server that captures the interaction between the number of vehicles in a transport segment and the effective vehicle speed. Using a non-linear traffic flow model, we show that the throughput reductions due to vehicle congestion can be as large as 85%. Hence, the effect of vehicle congestion during internal transport cannot be ignored. The model can also be used to determine the appropriate number of vehicles required to achieve the required terminal throughput by explicitly considering the effect of vehicle congestion.

Sequencing of storages and retrievals is an important topic in the automated storage and retrieval system (AS/RS), which largely influences the throughput performance and the operational cost of an AS/RS. In this paper, the problem of sequencing the storages and retrievals in a flow-rack AS/RS with duration-of-stay storage policy is analysed and a two-step heuristic called the grouping-matching method is proposed for minimising the total travel time of operations. The proposed grouping-matching method assigns unit-loads into groups in the grouping step and matches groups and bins of flow rack in the matching step. Two grouping heuristics are designed for the grouping step. The matching subproblem is formulated as an assignment to be solved. Simulation experiments are conducted to evaluate the effectiveness and efficiency of the grouping-matching method and the two grouping heuristics used for the grouping subproblem.

The significance of schedule reliability as a particularly important logistic objective is indisputable. In comparison to the objectives WIP, utilisation and throughput time, the modelling of the schedule reliability is, however, not very advanced until now. This paper transfers the process capability indices used in quality management to schedule reliability and demonstrates two methods for depicting the schedule reliability as a function of its influencing parameters.

In the authors’ experience, students have difficulty in understanding the differences between production planning and control techniques. Presumably, current business managers, although they have heard about these systems, may also lack clarity on the differences between them. We outline manual games for simulating production runs in four systems (Materials Requirements Planning, Just-In-Time, Theory of Constraints and CONWIP) to give managers and students’ insight into the mechanics of different production planning control techniques. We then provide excel-based simulation tools to allow users to vary parameters for each system and see the impact on inventory and throughput. We believe that the combination of manual and excel-based games significantly enhances understanding of the systems as well as their differences.

Flow-rack is a multi-deep rack containing multi-row and multi-column slope bins. Traditionally, bins slope in the same direction in a flow-rack to make unit-loads slide from the storage face to the retrieval face driven by gravity, which cause unit-loads are stored to the storage face and retrieved from the retrieval face. In this paper, a bi-directional flow-rack (BFR) is designed, in which bins in adjacent columns slope to opposite directions. In each side of a BFR, unit-loads are stored in half of the bins and retrieved from the other half. Therefore, dual-command (DC) operations could be simultaneously performed on both faces and blocking unit-loads are re-stored to available bins on the same face directly. We develop a travel time model for BFR systems, which provides the throughput baseline for different configurations of BFR. A DC operation generation method is introduced for BFR systems. Simulation experiments are conducted to evaluate the effectiveness of the BFR travel time model, to compare the...

Multi-product systems with finite buffers and sequence-dependent set-up times are quite common in modern manufacturing industry. In practice, the distribution of machine processing time could be arbitrary, while in existing literature it is often assumed to follow an exponential distribution. In this paper, we develop an analytical method to study the multi-product manufacturing systems with non-exponential processing times. An embedded Markov chain model is constructed and two approximation methods, Gamma estimation and linear approximation, are proposed. The model is validated with high accuracy by numerical experiments and practical data from an automotive assembly system.

Over the past few decades, a considerable number of studies have been reported on assembly lines or less automated factories. Little attention has been given to implementing lean tools to a highly automated manufacturing environment. It is, therefore, necessary to make a more highly automated factory lean by considering both the manufacturing system variability and demand uncertainty. The purpose of this paper is to propose an effective lean tool to help practical lean participants successfully implement lean practices in a highly automated manufacturing environment. This study presents an example of how lean standard work is implemented and the throughput of a pacemaker workstation is improved by solving the low work-in-process buffer problem. A practical case from a photovoltaic module process with a semi-automated production line is used to illustrate the proposed method. The implementation results are promising. They showed a 37.5% labour reduction prior to the pacemaker workstation and a 304.7% incre...

This paper investigates the selection and assignment of workers to tasks based on individual learning and forgetting characteristics in order to improve system throughput. We examine the performance of five policies that rank and select workers using a learning and forgetting-based assignment to address the task allocation problem. We are interested in the interaction between the implemented policies and various factors such as the ratio of generalists to specialists in the workforce, the level of multifunctionality and the level of workforce heterogeneity. Results demonstrate that, when implementing cross-training, selecting workers based on a greedy prediction of system output is outperformed by other simpler policies based on prior expertise.

The re-entrant flow shop scheduling problem considering time windows constraint is one of the most important problems in hard-disc drive (HDD) manufacturing systems. In order to maximise the system throughput, the problem of minimising the makespan with zero loss is considered. In this paper, evolutionary techniques are proposed to solve the complex re-entrant scheduling problem with time windows constraint in manufacturing HDD devices with lot size. This problem can be formulated as a deterministic Fm | fmls, rcrc, temp | Cmax problem. A hybrid genetic algorithm was used for constructing chromosomes by checking and repairing time window constraints, and improving chromosomes by a left-shift heuristic as a local search algorithm. An adaptive hybrid genetic algorithm was eventually developed to solve this problem by using fuzzy logic control in order to enhance the search ability of the genetic algorithm. Finally, numerical experiments were carried out to demonstrate the efficiency of the developed approaches.

Capacity planning for large-scale high-tech manufacturing processes such as semiconductor manufacturing and thin film transistor-liquid crystal display (TFT-LCD) using simulation of an entire fabrication facility (fab) requires a large computational effort and thus few studies have been in real settings. To address the needs of a realistic problem, this study aimed to develop an effective approach based on a discrete-event simulation model for evaluating the throughput, cycle time and utilisation in an integrated fab to integrate manufacturing and transportation resources. In particular, we conducted an empirical study in a real TFT-LCD fab expansion facing a difficult capacity planning problem arising from the expectation that one or more bottlenecks may shift to different sites, including the transportation system between the incumbent and the expansion fabs. Different product-mix alternatives and feeding policies are investigated to determine the best fab configuration. The results have shown practical...

Given increased pressure to provide short delivery times, minimising customer order throughput time is a very important objective in warehousing operations. There are many factors that may affect the performance of an order picking system, such as layout of the warehouse, the storage strategy, the routing policy, the zoning method and the batching policy. In this study, we propose a simple travel time model and analyse the effect of order batching on the expected customer order throughput time with variable time window batching. In addition, we discussed the impact of some parameters on the batch size and the expected customer order throughput time. In the practice of Wuhan Dong Hon Logistics co. Ltd, the storage rack in the warehouse has two levels: the low storage level and the high storage level. These two levels are visited by pickers and forklifts, respectively. The classification improves the performance of order picking. In this study, we build the model based on this practice.

In this paper we analyse the loss of throughput rate of assembly line caused by slow pace of substitute workers (replacing absentees) having no prior experience in the required tasks. We proposed work-sharing mechanisms that improve the balance of the workload during the learning period. The proposed mechanisms add to the experienced neighbouring workers some of the workload of the inexperienced worker substituting an absentee. We call this workload ‘shared work’. After the performance of the substitute workers improves due to learning, the shared work is re-assigned to them (relieving their experienced neighbours). We provide analytic expressions for the line throughput rate, which is determined by sets of bottleneck workstations. These sets of consecutive workstations consist of the inexperienced workers replacing the absentees and the experienced workers assisting them during the learning periods. The decision variables of this model are: (1) the amount of shared work, and (2) the time in which the sha...

Productivity of professional service is difficult to measure, due to the high degree of customization, variable throughput time, and high degree of labor intensity. Using the complex design engineering for large construction projects as an example, this study reviews the common professional service productivity measurement problem of determining surrogate measures of inputs and outputs. This research was sponsored by the construction industry, and required a team of academic and construction executives to work closely to develop a procedure and a comprehensive empirical model for measuring engineering design productivity. The model addresses the complexity of productivity estimation arising from the interactions among the multiple outputs and variability of labor hours, both requiring surrogate measures. The mathematical model was statistically estimated using data from a large number of design engineering organizations. The statistical results and the model were externally validated in several organizati...

Automatic material handling system (AMHS) is becoming more important in 300 mm wafer fabrication factories (fab). Effective and efficient design and control of AMHS has become more critical particularly in capacity planning. The major concept of the AMHS capacity determination model is to maintain the originally designed optimal production throughput or cycle time of products. In order to maintain fab’s throughput or cycle time of products, WIP (work in process) portfolio of the constraint or the fastest workstation should be kept. Based on this concept, a GI/G/m queuing model based on FCFS (First-come-first-serve) dispatching rule of AMHS is applied to determine the required number of vehicles. Basically, products should be transported to the specific workstation (constraint or fastest workstation) before the workstation finishes the existing process; therefore, sufficient WIP in front of this specific workstation should be kept. Under this condition, the probability that transportation time exceeds prod...

Automated storage and retrieval systems (AS/RS) are devices that allow intensive storage of materials. They can improve the supply chain performance, assuring more available volume for storage, lower labour costs and higher handling throughput of warehousing. Furthermore, the automated control allows the probability of errors in storage and retrieval to be minimised, along with the probability of product damage during movements. The purpose of the paper is to find the best solution in order to find the optimal dwell point policy, among different rules, able to minimise the travel time and distance travelled by stacker cranes, and consequently warehousing costs. An original and innovative model was developed in order to investigate the dwell point position for random allocation of unit loads. A software platform was developed to validate the proposed model by computer simulations. The performance of the system was analysed in a parametric/continuous way, varying at the same time the number of spans and levels, the height of the input/output point and the interval between requested missions. The results show that the developed model allowed convenience areas to be identified among the policies in which the travel time, distance travelled, and consequently warehousing costs are minimised, by varying different parameters. © 2013 Copyright Taylor and Francis Group, LLC.

This paper presents a solution procedure for reliable production lines with service times distributed according to an exponential distribution, based on a Markovian formulation with a Kronecker structured representation (sum of tensor products). Specifically, structured Markovian formalisms are used to reduce the impact of the well-known state explosion problem associated with other methods of solution. Such formalisms combined with the Kronecker representation deliver memory efficiency in storing very large models, i.e. models with more than states. The exact steady-state solutions of these models may be obtained using efficient existing software packages. The proposed solution procedure is illustrated with two detailed examples, and generalised with a model construction algorithm. The computed throughput for several examples of production lines with perfectly reliable machines, as well as the computational costs in terms of CPU time to solve them with PEPS2007 and GTAexpress software packages, are also ...

Production systems are often managed to maximise their production rate ( ). In some cases, this leads to excessive work-in-process and, as a result, long production lead time ( ). This issue is of particular importance in systems with ‘unlimited’ buffer space, where may also become unlimited. The question addressed in this paper is: What should be the release rate of raw materials so that the desired is obtained, while is maximised? We answer this question for serial lines with infinite buffers and machines obeying the Bernoulli reliability model. Specifically, given a serial line, we quantify the set of attainable s (feasible set), and for each point in the feasible set provide the release rate (as a function of machine parameters) that guarantees the desired lead time, while maximising the production rate. In addition, we offer a feedback control law that enforces the desired system behaviour. The development is based on a recursive aggregation procedure that leads to analytical estimates of . The accur...

This article presents the results of a study investigating the performance of unpaced unreliable production lines (i.e. subject to breakdown) that are unbalanced in terms of their buffer storage sizes. Simulation is carried out for five, eight and 10 station lines with mean buffer space set at two, four and six units. Buffer capacity is allocated in different configurations for each of these lines. Performance indicators on throughput, idle time and average buffer level are analysed using a range of statistical tools, and relationships between the independent and dependent variables are determined. Overall results show that the best patterns for unreliable lines in terms of generating higher throughput rates (or lower idle times) as compared to a balanced line are those where total available buffer capacity is allocated as evenly as possible between workstations. In contrast, concentrating more buffer capacity towards the end of the line gives best average buffer level results.

In this paper, we introduce two application studies of Production Systems Engineering (PSE) at a Toyota manufacturing plant in Georgetown, Kentucky, USA. Specifically, we study the engine assembly line and the block production line in powertrain manufacturing. By applying PSE methods, analytical models have been developed and validated using the data collected on the factory floor. It is shown that the models provide accurate estimates of line throughput compared with that observed in actual production. Using these models, we then develop methods for continuous improvement. In the engine assembly line, we identify the system bottlenecks, which are the machines impeding system throughput in the strongest manner, and improve line performance through bottleneck elimination. In the block production line, we evaluate the lean buffers, which have the smallest buffer capacity necessary and sufficient to achieve the desired line throughput. The results of these studies have been successfully implemented on the fa...

In this paper, we consider unpaced synchronous transfer lines producing a single product. The transfer line stations are arranged in a series configuration, have no buffers, and are subject to operation-dependent failures. Throughput is an important performance measure for transfer lines, and we have adopted that measure. Analytical methods for determining capacity of such transfer lines are available only for the simplest systems, but we show Monte Carlo simulation to be a fast, flexible, easy, and accurate method of estimating throughput in lines of any length and having a wide range of operating characteristics.

Many organisations suffer from a self-inflicted wound – they attempt to do too much! As a result, nothing is done well and profits suffer. Our article addresses this problem by suggesting that managers should focus on a subset of their current initiatives – a subset selected to maximise returns without overstraining resources. We address the following issues: What are the symptoms of work overload? How does an excessive workload adversely impact the bottom line? How can managers determine the throughput capacity of their organisation? What can be done to address the problem of excessive workload? Many, if not most, organisations attempt to operate beyond their capacity, with the result that inefficiencies abound, deadlines are missed and profitability drops. Based on research and consulting experience in many companies, our paper explains the basic concepts of ‘the 25/25’ approach to project portfolio management – an approach designed to increase profitability by concentrating only on the work that is ess...

This paper analyses the effects of absenteeism in assembly lines. The analysis shows that assigning temporary workers as substitutes for absentees has a major potential for generating bottlenecks. Such a bottleneck typically appears when an inexperienced worker replaces an absentee worker at their position. The inexperienced worker starts their learning curve, and for the initial period is significantly slower than other stations, and therefore is a bottleneck. The paper analyses the effect of typical absenteeism rates on the throughput, and shows it has strategic magnitude. This is verified using simulation. The effect of the absenteeism and turnover on the throughput is found to be related to the cycle time, and the amount and rate of learning. The paper discusses the simulation results, staffing requirements, strategies for overcoming absenteeism, and future research directions.

Production planning (or product design) in the steel industry needs specific, sophisticated procedures in order to guarantee competitive plant performance. This paper describes an integrated tundish planning problem, considering the steelmaking-continuous casting-hot rolling and other downstream integrated technical constraints, and a multi-objective optimisation model is proposed with the objective to optimise the number of tundish, the additional cost of technical operations and the throughput balance to each flow. Also, instead of using traditional metaheuristic algorithm or artificial intelligence (AI)-based heuristic approaches, this paper develops two new approaches, the improved variable neighbourhood descent (IVND) search method and improved reduced variable neighbourhood search (IRVNS) method, by introducing the iterated local search into local search to the problem described above. The performance of IVND and IRVNS are analysed based on changing the number of local iteration and weights of objec...

In this paper, we address the problem of defining the product mix in order to maximise a system's throughput. This problem is well known for being NP-Complete and therefore, most contributions to the topic focus on developing heuristics that are able to obtain good solutions for the problem in a short CPU time. In particular, constructive heuristics are available for the problem such as that by Fredendall and Lea, and by Aryanezhad and Komijan. We propose a new constructive heuristic based on the Theory of Constraints and the Knapsack Problem. The computational results indicate that the proposed heuristic yields better results than the existing heuristic.

The line–cell (or line–seru) conversion is an innovation of assembly systems that has received less attention. Its essence is dismantling an assembly conveyor line and adopting a mini-assembly unit, called seru (or cell). In this paper, we discuss how to do such line–cell conversions, especially focusing on assembly cell formation (ACF) and assembly cell loading (ACL). We perform 64 arrays of full factorial experiment analysis that incorporate three factors: work stations, product types, and product lot sizes. We construct a two-objective line–cell conversion model that minimises the total throughput time (TTPT) and the total labour hours (TLH). Three non-dominated solutions obtained from the two-objective model are used to evaluate the performance of the line–cell conversion. By investigating the experimental results of the ACF and the ACL, we summarise several managerial insights that could be used to help successful line–cell conversions.